Blow moulding machines are sufficiently known from the prior art. Hollow bodies with volumes between 0.05 and 20 liters are typically produced of thermoplastic polymers in these blow moulding machines. Typical blow-moulded parts are bottles, as well as transport, packaging and storage containers. At present, it is preferred to use polyethylene terephthalate (PET) for bottles and containers with a content up to 20 liters.
Blow moulding machines that are configured, for example, for PET bottles are known in different variations (with and without mechanical stretching rod). In this case, the tubular or bell-like blow nozzle is directly attached, for example, to the opening of a preform or to a transporter carrying this preform in a gas-tight manner in order to connect the preform to low-pressure blowing air, high-pressure blowing air or an air vent opening. The pressurization of the preform with low-pressure blowing air or high-pressure blowing air is usually realized with a plurality of control valves that are connected to the blow nozzle.
Nowadays, the industrial stretch blow moulding machines currently available on the market reach production rates of up to 80,000 bottles per hour, which is the reason why of course particularly fast control valves need to be constructed for the pressurization of the preform with low-pressure blowing air or high-pressure blowing air, respectively. In this context, it is important that the build-up and also the discharge of an air pressure up to 40 bar (high-pressure blowing air) are accomplished as fast as possible. In one known method, this is achieved by maintaining the so-called “dead air volume” as small as possible. The term “dead air volume” refers to the air column that is situated between the control valve and the preform to be blown. Since this “dead air volume” is deaerated with the air volume blown into the bottle, it furthermore causes a waste of high-pressure blowing air and therefore a waste of energy.
In this context, it is referred, for example, to U.S. Pat. No. 7,927,093 B2 that already deals with the reduction of the “dead air volume.” To this end, U.S. '093 B2 proposes to detachably mount a valve housing, that contains all required control valves, on the front side of the housing block of the blow nozzle. However, this measure is not only intended for achieving a reduction of the dead air volume; in fact, the detachable mounting of the valve housing on the housing block of the blow nozzle significantly simplifies the maintenance of the blow moulding machine.
The device for controlling blowing mediums in a stretch blow moulding machine known from the prior art has the disadvantage that it can only be produced with substantial constructive effort. In particular, it is necessary to fabricate two housings (valve housing, housing block of the blow nozzle) that are almost perfectly adapted to one another and to connect these housings to one another in compliance with minimal tolerances. Furthermore, the interface between the valve housing and the housing block needs to be elaborately sealed in the known device in order to prevent leakages.
Based on the above-defined problem, it is the object of the present invention to disclose a device for controlling blowing mediums in a stretch blow moulding machine that minimizes the dead air volume between the control valves and the blow nozzle and also features a particularly simple construction.